1. Field of the Invention
The field of the present invention relates generally to chemical baths in which metal ions build up over a period of time and must be periodically removed, and more particularly to such systems providing for coating materials, such as metals including steel, with a paint coating via a chemical reaction, in which systems an autodeposition composition bath is periodically stabilized by removing therefrom dissolved and/or dispersed multivalent metal ions accumulated over a period of operation.
2. Discussion of Related Art
Autophoresis and electrophoresis are two known processes for coating objects, particularly those fabricated from metallic material, with a coating composition. The electrophoresis effect provides for electrodeposition through the use of an electric field to control the movement of charged organic molecules to a workpiece serving as one electrode of a typically two-electrode system. The magnitude of electrical current and time of application is controlled for coating the workpiece to a desired thickness. The autophoresis effect permits an autodeposition coating process to be carried out via control of the de-stabilization and deposition of high-molecular-weight negative or neutrally-charged latex polymer particles, for example, onto a workpiece having a metallic surface that is chemically treated to produce positively charged ions at the surface of the workpiece which attract the oppositely or neutrally charged particles of coating composition. The parts to be coated are typically dipped into a coating bath containing the desired coating composition. Workpieces of iron, steel, galvanized metal coated with zinc, and so forth, at least about the outer surfaces of the workpiece, can typically be coated via an autodeposition coating process.
A problem in systems carrying out an autodeposition coating process is that over a period of time metal ions having a valence of two or higher (multivalent ions), dissolve and/or disperse into the bath or autodeposition composition, increasingly reducing the effectiveness of the autodeposition coating process. As the metal ions increase in concentration in the autodeposition composition, the quality of the coatings produced on the workpieces diminishes to the point where the coating composition or autodeposition bath must be replaced, or a portion of the bath must be removed and new uncontaminated coating composition added, to reduce the concentration of the metal ions, for permitting the autodeposition coating process to continue.
In order to satisfy a recognized need in the field of the present invention, the present inventors conceived and developed a substantially automated system for periodically removing contaminants from coating composition baths used in autodeposition processing. In designing the present system, the inventors recognized the need to provide that substantially all of the autodeposition bath or coating composition be utilized in coating parts, compared to prior systems which wasted costly quantities of the autodeposition baths due to contamination thereof after a period of use forcing disposal of the same. The present inventors further recognized the requirement to provide a system which substantially minimizes the production of waste products harmful to the environment. By designing a substantially automated system for autodeposition processing, maximum economics are obtained through the use of substantially all of the costly autodeposition bath or coating composition material.
The present inventors recognized that it is contrary to prior teachings to pass any solution containing particulates, such as latex and pigment included in AUTOPHORETIC or autodeposition baths through an ion exchange (IEX) column. They conceived the present system to accomplish this operation, and overcame the problems in the prior art such as clogging of IEX columns by autodeposition baths.